EP0979988B1 - Method of evaluating relative linear movements between permanent magnets and sensors - Google Patents

Description

The invention relates to measuring methods for contactless magnetic Detection of linear relative movements between Permanent magnets and electronic sensors according to the generic terms of claims 1 and 12. With the aid of these methods linear movements should be contactless by means of magnetic Interaction between one or more permanent magnets and magnetic sensors can be detected and evaluated.

The measurement of linear movements takes place, for example, in machine tools, in pneumatics, in automation technology and robotronics as well as in the automotive sector. A non-contact Movement detection offers the advantage of Freedom from wear. Among the non-contact measurement methods are the most common optical and magnetic. During the optical process due to the small wavelength guarantee a very high accuracy of the light, magnetic methods are far less sensitive to pollution and damage, especially due to the fact that magnets and sensors completely in a non-magnetic shell can be encapsulated (see e.g. Dettman F. et al. "Magnet-based and yet highly precise. Length measurement with magnetoresistive microsystems ", electronics, DE, Franzis Verlag GmbH, Munich Vol 44, No. 25, pages 86-88, 90-92).

Magnetic processes generally use a multi-pole Magnetic stripe used as a donor magnet. By capturing the pole transitions by an electronic magnetic field sensor an incremental shift is detected, the means that after counting the zero crossings a digital one is obtained Signal. Hall sensors, for example, magnetoresistive elements or inert gas switches or Reed relay used.

In the case of the processes with multipole magnetic strips, the Resolution by the pole width and this in turn by the Distance between sensor and magnetic stripe limited. There are the ability to increase the resolution by increasing the amount Field strength between the poles evaluated and the location is interpolated between two pole passes. Nearby the field maxima, however, the change in field strength is small, so that the measurement accuracy is limited here.

Another known method for direct analog measurement the shift at which the measurement signal is in contrast to the Incremental measurement changes continuously with the shift, consists in measuring the radial field strength in addition an axially magnetized bar magnet, in which the sensor is moved parallel to the bar axis. In the area between The measured field strength varies continuously in the two pole poles between a maximum at the north pole and an equally strong but reversed sign at the level of the south pole. This area can be measured from the Field strength clearly infered from the position become. This method of measurement has two limitations, the Limit accuracy and applicability. So becomes the measured field strength due to temperature fluctuations, Positional tolerances of the sensor in relation to the rod axis and Tolerances of the sensor itself affect what is an apparent Pretending shift. Second is the measurable area limited to the transition between two poles, since outside a reversal of the flow direction occurs in this area, which is an ambiguous assignment of field strengths to the sensor position causes.

The invention is based, measuring methods according to the task the preamble of claim 1 with a magnet and sensor arrangement and to create evaluation methods with which Relocations without the aforementioned restrictions in be detected more easily, reliably and precisely can.

This object is achieved according to the invention in a first method variant solved in that for the detection of the linear Relative movements by means of the electronic sensors one location two mutually perpendicular field components be recorded, the quotient evaluated for position detection becomes.

In a second variant of the method, the method according to the invention can be used Measurement procedures can also be carried out so that for detection the linear relative movements by means of the electronic Sensors in two places two perpendicular to each other Field components are recorded, their quotient for position detection is evaluated.

Particularly advantageous developments of the invention Methods are in claims 2 to 11 or 13 and 14 characterized.

With the measuring method according to the invention are in one place detected two orthogonal field components from their relationship the position is calculated back. This has the advantage that in areas where a field component has a Assumes extreme value and therefore not small shifts be detected, the other field component on shifts strongly reacts, so that an equal in the entire measuring range high measuring accuracy is given.

Furthermore, these measuring methods according to the invention are very much less sensitive to a change in the absolute magnetic field strength, since ratio numbers between the Field components can be used for position detection.

It is particularly advantageous if one for signaling axially magnetized bar magnet is used, at least two sensors arranged laterally from it the radial and detect the axial field component. It can be useful a permanent magnet made of an AlNiCo material for signaling be used.

In a modified embodiment, the Signaling but also a diametrically helical magnetized bar magnet can be used, the side of which sensors arranged the field components vertically to the rod axis.

However, particularly precise measurement results can also be obtained in this way be that for signaling two diametrically helical oppositely magnetized bar magnets are used be arranged in a plane parallel to each other over which the sensors are perpendicular to the field components capture the bar axes.

In a comparison, simplified embodiment can instead of the two oppositely magnetized bar magnets a profile magnet with a central web part for signaling and two thickened outdoor areas is used at the outer areas are magnetized in a helical shape and vertically the two field components via its web sensors to the rod axes.

This profile magnet can be in an inexpensive embodiment made of a plastic-bound isotropic magnetic material consist of and by a magnetizing arrangement two screwdriver-shaped conductors, namely one running energized conductor and a returning energized conductor, magnetized above the profile by a current pulse become.

In a further embodiment, four or more diametrically helical magnetized bar magnets used in parallel on a pitch circle the sensor axis are arranged.

To expand the measurable measuring range, you can use these Process variants using electronic sensors two orthogonal field components of one or more diametrically helical magnetized bar magnets or equivalent Profile magnets are detected, with quotient and absolute strength of the field components for position detection be evaluated in such a way that the arc tangent from the Ratio of field components to fine-tune the position and the absolute field strength corresponds to a rough survey the number of passes made from 360 ° to 0 °. Here it is possible to continuously increase the absolute Field strength due to a decrease in the distance from encoder magnets to sensors, preferably by tilting them slightly of motion axis and magnetic axis.

A continuous increase in the absolute field strength can in a modified embodiment but also by Change in cross section of the encoder magnet or magnets Magnetic axis are generated.

A further improvement in the measurement results can be found in the above mentioned second method variant after the secondary Claim 12 can further be achieved in that the radial field components of two sensors at two points of a diametrically helical magnetized bar magnet be measured that the two sensors are coupled and moved parallel to the central axis of the rod-shaped transmitter magnet and that the radii from the magnetic axis to the Sensors are at right angles to each other.

Finally, it is in both variants of the invention Measuring method according to claim 14 also possible that instead of diametrically helical magnetized bar magnets one or more twisted bar magnets with square Cross section of an anisotropic plastic-bound elastic Magnetic material with the magnetization perpendicular to Bar axis can be used.

Fig. 1

eine erste Meßanordnung mit überlagertem Diagramm der radialen und axialen Feldkomponenten in ihrem Verlauf,

Fig. 2

eine gegenüber Fig. 1 abgewandelte zweite Ausführungsform einer Meßanordnung ebenfalls mit überlagertem Diagramm,

Fig. 3

eine weitere abgewandelte Ausführungsform einer Meßanordnung mit zwei parallelen Stabmagneten und mit überlagertem Diagramm,

Fig. 4

noch eine weitere Meßanordnung mit zwei parallelen Stabmagneten und mit überlagertem Diagramm,

Fig. 5

eine weitere Ausführungsform eines Stabmagneten mit zwei im Querschnitt verdickten parallelen Außenbereichen mit Magnetisierspule für eine derartige Meßanordnung und

Fig. 6

eine Meßanordnung mit zwei Sensorelementen um einen Stabmagneten aus einem kunststoffgebundenem isotropen Hartferritwerkstoff und mit zugehörigem Diagramm.

Particularly advantageous exemplary embodiments for the measuring method according to the invention and the sensor and magnet arrangements used therefor for the contactless magnetic detection of linear relative movements are shown schematically in the drawing. Show it

Fig. 1

a first measuring arrangement with a superimposed diagram of the radial and axial field components in their course,

Fig. 2

1 modified embodiment of a measuring arrangement also with a superimposed diagram,

Fig. 3

another modified embodiment of a measuring arrangement with two parallel bar magnets and with a superimposed diagram,

Fig. 4

yet another measuring arrangement with two parallel bar magnets and with a superimposed diagram,

Fig. 5

a further embodiment of a bar magnet with two parallel outer regions thickened in cross section with a magnetizing coil for such a measuring arrangement and

Fig. 6

a measuring arrangement with two sensor elements around a bar magnet made of a plastic-bound isotropic hard ferrite material and with an associated diagram.

In the bar magnet 1 shown in FIG. 1, a sensor element 3 is displaceable parallel to the bar axis 2 along a straight line 3a, which in the example _detects a radial field component B _rad and an axial field component B _axi .

The bar magnet 1 has a diameter D = 10 mm and its bar axis 2 is at the same radial distance of r = 10 mm from the sensor element 3. The two field components B _rad and B _{axi are shown} in their course in the superimposed diagram. While the radial component B _{rad can be used} in a known manner for position detection between the poles (in the example over a length of z = 60 mm) for position detection, the angle alpha can be determined from the radial and the axial component via the relationship alpha = arc tan (B wheel / B axi ) be determined, which allows a clear position detection beyond the area between the poles.

Since the two field components B _rad and B _axi are influenced in the same way by temperature _or position tolerances, the quotient of the two values is primarily not falsified by this. Magnetic materials with a magnetic relative permeability greater than 2 are particularly suitable for such arrangements, since the angular profile is relatively uniform. Alloys made of Al, Ni, Co and Fe (so-called AlNiCo alloys) are therefore particularly suitable for this process.

This method is according to the invention in accordance with FIGS. 2 to 6 have been further developed that instead of an axial magnetized bar magnets 1 one or more bar magnets be used which is a diametrically helical Have magnetization, so similar to those above measuring rulers described any measuring range can be painted over.

Such a diametrical magnetization, as with the bar magnet 1 shown in Fig. 2 is made by special magnetizing coils with a screwdriver-shaped current curve imprinted in a pulse discharge. Without magnetizing coil can a magnet with comparable characteristics from one elastic plastic-bonded bar magnet with square Cross section can be produced. Such a magnet that is magnetized transversely to the rod axis, can be twisted in such a way that a helical magnetization is shown is. This allows anisotropic in a simple manner Use magnetic materials.

Some particularly advantageous measuring methods according to the invention are in the following examples in connection with Fig. 2 to 6 described.

Example 1:

A bar magnet made of a plastic-bound rare earth material, as it is offered by the Magnetfabrik Bonn GmbH under the trademark Neofer 62 / 60p, with a length of L = 100mm and a diameter of D = 10mm, is magnetized diametrically clockwise, with north and South poles (N and S) are stamped in stripes on the outer diameter with a pitch of 60mm per revolution by a corresponding magnetizing coil. At a distance of r = 10mm from the rod axis 2 of the round bar magnet, a sensor element 3 moves parallel to the rod axis, with which a radial field component B _rad and a tangential field component B _tan standing perpendicular to it (in FIG. 2 perpendicular to the plane of representation) are measured. The two field components B _rad and B _tan are plotted in FIG. 2 in the superimposed diagram as a function of the position relative to the bar magnet 1. With this arrangement, the position can be derived from the angle alpha between field direction and radial direction over a range of 60 mm according to the above formula.

Example 2:

Two bar magnets 1 made of a plastic-bonded rare earth material, as under the trademarked name Neofer 62 / 60p offered by Magnetfabrik Bonn GmbH with a length of L = 100mm and a diameter of D = 10mm are diametrically clockwise helical magnetized, with north and south poles in stripes on the outside diameter with a pitch of 60mm per revolution imprinted by an appropriate magnetizing coil become. The two bar magnets 1 are at a distance of d = 20mm arranged parallel to each other so that the same poles face.

At a distance of r = 10mm above the plane spanned by the two rod axes 2 and centrally between the rod magnets 1, a sensor element 3 moves along the straight line 3a parallel to the rod axis 2, with which a radial field component B _rad and a tangential field component B standing perpendicular to it _tan (as in Fig. 2 perpendicular to the plane of representation) can be measured. The two field components B _rad and B _tan are plotted in FIG. 3 in the superimposed diagram as a function of the position of the sensor element 3. With this arrangement, the position can be derived from the angle alpha between field direction and radial direction over a range of 60 mm according to the above formula.

In contrast to Example 1, this results in a linear one Dependence of the angle alpha on the position of the sensor element Third

Are according to the two bar magnets 1 below the movable sensor element 3 two further bar magnets above of the sensor element at the same distance and with the opposite Magnetization arranged, so you get in the Sensor axis field values of double strength, which at light Deviations from the sensor axis remain unchanged, so that this arrangement is particularly insensitive to positional tolerances the sensors is.

Example 3:

With otherwise the same structure as in Example 2, the diameter of the stanchion magnets 1 increases linearly from D end to the other end from D = 9 mm to D = 11 mm, so that the magnetic rods have a slightly conical shape. 4 shows the arrangement with the corresponding field components B _rad and B _tan .

This arrangement also allows the position to be determined a coarser position determination via the angle alpha about the recorded absolute field strength. By considering ambiguity of both signals can be excluded, which infer from the angle alpha to the position results if an area larger than 60mm is covered will, that is if the screw of magnetization more than describes a full revolution.

Example 4:

A profile magnet is a cost-effective variant, for example 3 10 made of an isotropic material used on the two outer sides of a central web part 10a the two 3 and 4 comparable thickenings 10b and bears 10c. Through a screwdriver-shaped magnetizing coil becomes a current pulse from the discharge of a capacitor bank used to magnetize the profile magnet 10. The arrangement shown in Fig. 5 shows the profile magnet 10 with a current-carrying conductor 11 and one returning current-carrying conductor 12.

The profile magnet 10 then takes the place of the two bar magnets 1 of Fig. 3.

The absolute field strength depends on the magnetic material used changed compared to example 2, but the course accordingly.

Example 5:

A bar magnet 1 made of a plastic-bound isotropic Hard ferrite material as it is protected under the trademark law Description Sprox 3 / 19p from the Magnetfabrik Bonn GmbH is offered, with a length of L = 100mm and a Diameter of D = 10mm is diametrically clockwise helical magnetized, with north and south poles in stripes on the outside diameter with a pitch of 60mm per revolution imprinted by an appropriate magnetizing coil become.

At a common distance of r = 10mm from the rod axis 2 of the Round bar magnets 1 and perpendicular to each other Coupled radii move parallel to the axis of the rod the straight line 3a two sensors 3.1 and 3.2, with which the radial Field components B1 and B2 measured perpendicular to each other become. The two field components B1 and B2 are shown in Fig. 6 in the superimposed diagram depending on the position applied. This arrangement can cover an area of 60mm the position from the angular ratio of the measured field components also according to the above formula be derived.

List of reference numbers

1

bar magnet

2

rod axis

3

sensor element

3.1

sensor element

3.2

sensor element

3a

Just

10

profile magnet

10a

web member

10b

thickening

10c

thickening

11

current-carrying conductor

12

returning current-carrying conductor

B

magnetic flux density

B _rad

radial field component of B

B _axi

axial field component of B

B _tan

xtangential field component of B

B1

xradial field component of B

B2

radial field component of B

N

North Pole

S

South Pole

Claims (14)

1. Measuring method for non-contact magnetic detection of linear relative movements between permanent magnets and electronic sensors by means of a sensor and magnet assembly, characterised in that, to detect the linear relative movements by means of the electronic sensors at one point, two field components at right-angles to one another are detected, and their quotient is used for position detection.
2. Measuring method according to claim 1, characterised in that an axially magnetised bar magnet (1) is used for signal transmission, with sensors arranged to either side of it detecting the radial and axial field components.
3. Measuring method according to claim 1 or 2, characterised in that a permanent magnet made of an AlNiCo material is used for signal transmission.
4. Measuring method according to claim 1, characterised in that a diametrically helically magnetised bar magnet (1) is used for signal transmission, with the sensors arranged to either side of it detecting the field components at right-angles to the bar axis (2).
5. Measuring method according to claim 1, characterised in that two bar magnets (1) with diametrically opposed helical magnetisation are used for signal transmission, being arranged parallel to one another in a plane over which the sensors detect the field components at right-angles to the bar axes (2).
6. Measuring method according to claim 1, characterised in that for signal transmission a profile magnet (10) with a central web section (10a) and two thickened outer sections (10b, 10c) is used, in which the outer sections are helically magnetised and over the web of which sensors detect the two field components at right-angles to the bar axes (2).
7. Measuring method according to claim 6, characterised in that the profile magnet (10) is made of a plastic-bound isotropic magnetic material and is magnetised over the profile by a current pulse, by means of a magnetising assembly of two screwdriver-shaped conductors, namely a conductor (11) fed with inwards current and a conductor (12) fed with return current.
8. Measuring method according to claim 1, characterised in that for signal transmission four or more bar magnets (1) magnetised diametrically and helically are used, and are mounted parallel on a graduated circle around the sensor axis.
9. Measuring method according to claim 1 or any of claims 4 to 8, characterised in that by means of electronic sensors two orthogonal field components of one or more bar magnets (1) or corresponding profile magnets (10) magnetised diametrically and helically are detected, with the quotient and absolute strength of the field components being analysed for position detection in such a way that the arcus tangens from the ratio of the field components gives the fine detection of position and the absolute field strength a rough detection according to the number of passes made from 360° to 0°.
10. Measuring method according to claim 9, characterised in that a continuous increase in absolute field strength is generated by a reduction in the distance between transmitter magnets and sensors, preferably by slight tilting of movement axis and magnet axis.
11. Measuring method according to claim 9, characterised in that a continuous increase in absolute field strength is generated by a change in cross-section of the transmitter magnet or magnets across the magnet axis.
12. Measuring method for non-contact magnetic detection of linear relative movements between permanent magnets and electronic sensors by means of a sensor and magnet assembly, characterised in that, to detect the linear relative movements by means of the electronic sensors at two points, two field components at right-angles to one another are detected, and their quotient is used for position detection.
13. Measuring method according to claim 12, characterised in that, by means of two sensors at two points the radial field components of a bar magnet (1) magnetised diametrically and helically are measured, that the two sensors are coupled and moved parallel to the centre axis of the bar-shaped transmitter magnet, and that the radii from the magnet axis to the sensors are at right-angles to one another.
14. Measuring method according to any of claims 1 and 4, 5, 8 to 11 or according to claims 12 and 13, characterised in that, instead of bar magnets (1) magnetised diametrically and helically, one or more twisted bar magnets with square cross-section, made from an anisotropic plastic-bound elastic magnetic material with magnetisation at right-angles to the bar axis (2), are used.

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